JPH04310984A - Developing device - Google Patents

Abstract

PURPOSE:To develop a latent image having sharpness, excellent gradation, and a sufficient image density without having base fogging and irregularities at low cost by a developing roller not damaging a photosensitive body. CONSTITUTION:The developing roller 20 is composed of the conductor part 21 of a foamed layer and the dielectric part 21 formed in a foamed cell, and the alternate bias of 500<=peak to peak voltage (vp-p)<=1500(v) is applied to a developing part 80 with a photosensitive body 10. At this time, toner is alternately soared up between the developing bias 80 and the photosensitive body by a difference in the electrostatic charge of the conductor part and the dielectric part and the transfer ratio of the toner is increased together with gradation.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides an image bearing member carrying an electrostatic latent image and a developer carrying member carrying a developer facing each other in a developing section, and applying a bias to the developing section by a bias applying means. The present invention relates to a developing device that performs development.

0002

2. Description of the Related Art Image forming apparatuses such as electronic copying machines, printers, and facsimile machines that form electrostatic latent images on image carriers and visualize them using developers to obtain recorded images use powdered developers. Dry type developing devices are widely used.

[0003] As such powdered developers, two-component developers containing toner and carrier and one-component developers that do not contain carrier are known, but the former two-component developer is not used. Although the two-component development method that was previously used can produce relatively stable and good recorded images, it is prone to carrier deterioration and the mixing ratio of toner and carrier to fluctuate, making the maintenance of the device complicated and tending to increase its size. become.

[0004] For this reason, a one-component developing system using a one-component developer free from such drawbacks is attracting attention. One-component developers include those consisting only of toner and those made by externally adding an auxiliary agent to toner as needed. Toners include magnetic toner, in which magnetic powder is kneaded into each toner particle itself, and non-magnetic toner, which does not contain magnetic material.

[0005] In this case, since nonmagnetic materials are generally opaque, when a color image including full color or multicolor is formed using magnetic toner, the developed visible image becomes unclear, making it difficult to obtain a vivid color image. Can not. Therefore, especially for color development, it is desirable to adopt a one-component development method using non-magnetic toner.

By the way, in a developing device employing a one-component developing method, a one-component developer is carried on a developing roller, which is a developer carrier, and transported, and the developing roller and the image carrier are opposed to each other. In the developing section, the electrostatic latent image formed on the image carrier is visualized using a developer, but in order to form a high-quality visible image with a predetermined density, a large amount of sufficiently charged toner must be used. It is necessary to transport it to the developing section.

[0007] When using magnetic toner, it can be supported using the magnetic force of a magnet installed in the developing roller, so the above requirements can be met relatively easily. However, when using a non-magnetic one-component developer,
Since this toner cannot be carried on the developing roller by magnetic force, it becomes difficult to transport a large amount of sufficiently charged toner. Various countermeasures against this have been proposed in the past.
For example, Japanese Patent Laid-Open No. 61-42672 discloses that a dielectric (insulator) layer is laminated on the surface of a developing roller, and a developer supplying member made of, for example, a sponge roller is brought into pressure contact with the layer, and both A method has been proposed in which the toner particles are frictionally charged to have opposite polarities, and the non-magnetic toner charged to the opposite polarity to the dielectric material is electrostatically attached to the dielectric material, and the toner is transported to a developing section.

However, even with this method, it is not possible to sufficiently increase the strength of the electric field formed near the dielectric surface, so it is difficult to carry a large amount of toner on the surface of the developing roller, and the toner cannot be transported to the developing section. Due to the insufficient amount of developer, it is difficult to form a visible image with high density.

[0009]Also, a configuration in which an electric field is applied between the developing roller and the developer supplying member in a direction in which the non-magnetic toner is electrostatically transferred toward the developing roller is also known. However, it is difficult to make a sufficient amount of toner adhere to the developing roller.

[0010] As the toner supply member, 102
~106 Ω・cm conductive foam (JP-A-60-22
9057), elastic body with skin layer (JP-A-60-2
29060 Publication), Fur Brush (Japanese Unexamined Patent Publication No. 61-42
It has been proposed to use a metal body with an uneven surface (Japanese Patent Application Laid-Open No. 60-53976), an insulating coated roller body (Japanese Patent Laid-Open No. 55-46768), etc. as a developing roller. JP-A-58-13278), an electrode roller having an insulator and a conductive surface (JP-A-53-36245), and the like have been disclosed.

Further, in a developing device using a non-magnetic one-component developer, JP-A No. 60-229057 uses a sponge roller, JP-A No. 62-229060 uses an elastic roller, and JP-A No. 61-52663 uses a sponge roller. Using a fur brush or the like, charge the toner by frictional charging between the toner and the replenishing member, and then electrostatically adhere the toner to the developing roller by the friction generated by contact with the developing roller. A method of developing a latent image on a photoreceptor by controlling a toner layer using a layer thickness regulating member has been proposed. In this case, various materials are used for the developing roller, such as insulating materials, medium resistance materials, and laminated materials.

[0012] In the systems shown in these prior art techniques, toner adhesion to the developing roller is performed by frictional charging between the toner replenishing member and the developing roller. It is difficult to obtain a certain charge,
As a result, toner adhesion is insufficient. Here, the toner adhesion amount and charge amount in the non-magnetic one-component development method will be explained as follows.

[0013] For black and white applications, emphasis is placed on the amount of charge, and its value is generally 10 to 20 μC/g, and if it is less than this,
The image quality will be poor in terms of background smearing and sharpness. On the other hand, regarding the amount of adhesion, the amount of adhesion on the developing roller is 0.1 to 0.3 mg/cm2, whereas 0.4 to 0.5 mg/cm2 is required on the transfer paper, and the speed of the developing roller is 0.1 to 0.3 mg/cm2. This amount of toner adhesion is obtained by increasing the speed of the photoreceptor to three to four times the speed of the photoreceptor. However, if the rotational speed of the developing roller is increased by 3 to 4 times, there is a problem in that the phenomenon of "toner from the trailing edge" occurs, that is, the density of the trailing edge of the image becomes higher when a solid area is developed. . In order to prevent this phenomenon, it is necessary to bring the speed of the developing roller closer to the speed of the photoreceptor, thereby increasing the amount of toner adhering to the developing roller, and reducing its rotational speed.

On the other hand, because color toner has a color characteristic of having a smaller degree of coloring than black toner, when trying to improve "from the trailing edge of the toner", the 0.
The amount of toner adhesion on the developing roller is required to be 8 to 1.2 mg/cm2. Regarding the amount of charge, in order to obtain a stable image, the amount of charge should be 5 to 20 μC/g (preferably 10 to 1
A value of 5 μC/g) is desired.

On the other hand, even if a large amount of sufficiently charged toner is attached to the surface of the developing roller, in order to develop the electrostatic latent image well, a bias must be applied to the developing section to remove the developer from the developing roller. In order to cause the developer to fly to the image carrier, it is necessary to apply a force stronger than the restraining force due to the electric charge to the developer on the developing roller.

However, in this type of development in which toner is caused to fly, if a method is used in which a bias is applied only in the direction of transferring the toner from the developing roller to the image bearing member, an image that lacks sharpness and gradation is produced. become. That is, at the edge of the image on the image carrier, the electric wire does not reach the developer carrier and wraps around to the non-image surface of the image carrier due to the charge induced in the non-image area. In some cases, the flying developer adheres very unreliably or does not adhere at all, resulting in an unclear image lacking sharpness at the edges of the image. In addition, the developer flies from the developer carrier to the image carrier when its potential exceeds a certain value and overcomes the restraining force of the developer by the developer carrier, so that the developer rapidly transfers after reaching a certain value. The amount increases, and the slope of the curve of image density versus electrostatic latent image potential becomes large, resulting in an image with poor gradation.

In order to solve this problem, a method has been proposed in which a voltage within a predetermined range is applied so as to form an alternating electric field in the developing section (see Japanese Patent Laid-Open No. 1013/1983).
. However, when an alternating electric field is applied in this way to cause the developer to fly alternately between the developing roller and the image carrier, the overall image density tends to decrease. Furthermore, if the frequency of the applied alternating electric field is too low, uneven density of the image will occur due to the bias cycle, while if the frequency is too high, the toner transfer time will be insufficient and the effect of flying development will be reduced.

[0018]

[Problems to be Solved by the Invention] As a method for solving these problems, the present inventors have previously developed a method for developing a non-magnetic developer carrier in which an auxiliary agent is externally added to a rotatably driven developer carrier. A one-component developer consisting of toner is supplied, the developer is carried on the surface of the carrier, and the latent image is conveyed in a development area where the latent image carrier and the developer carrier face each other. In a developing method in which an electrostatic latent image formed on a carrier is visualized by the developer carried on a developer carrier, the electrostatic latent image is made visible by selectively retaining an electric charge on the surface of the developer carrier. A large number of minute closed electric fields are formed near the surface of the carrier,
We proposed an image forming method in which the charged toner is attracted by this closed electric field, the developer is deposited on the surface of a developer carrier, and the electrostatic latent image is visualized by the carried developer.

According to this invention, since a large number of minute closed electric fields (microfields) are formed near the surface of the developer carrier, the electric field strength can be significantly increased compared to the conventional one, and sufficient charging can be achieved. Many advantages can be obtained, such as being able to carry a large amount of non-magnetic toner on the developer carrier and transport it to the development area.

However, even with such a method of forming a large number of microfields near the surface of the developer carrier, it is difficult to obtain a stable toner adhesion amount and charge amount over time depending on the developer carrier. There are cases,
Another problem is that the manufacturing process is complicated and the cost is high.

[0021] Furthermore, when the developer carrier is a rigid body,
In the contact development method, in which developer is brought into contact with a latent image carrier (photoreceptor) through toner, there is a risk that the developer carrier made of a rigid body may damage the latent image carrier (latent image carrier). (This tendency becomes even stronger when the body is made of a rigid body) and the contact area between the developer carrier and the latent image carrier is limited, making it difficult to obtain the desired toner adhesion amount and toner charge amount, and also to prevent development. Since the speed cannot be increased, there is a problem in that the developing efficiency decreases.

Therefore, the present invention solves the above problems, and
It is a developer carrier that can obtain stable toner adhesion amount and toner charge amount over time, and can be manufactured at low cost.
In addition to being equipped with a developer carrier that enables high-speed development without damaging the image carrier and has improved development efficiency, such a developer carrier provides sharp images with good gradation and sufficient density without background fog or unevenness. An object of the present invention is to provide a developing device capable of developing an electrostatic latent image on an image carrier.

[0023]

[Means for Solving the Problems] In order to solve the above problems, the invention of claim 1 provides a method for developing an image bearing member carrying an electrostatic latent image and a developer carrying member carrying a developer. In the developing device which performs development by applying a bias to the developing section by a bias applying means, the developer carrier has a dielectric section on its surface and a dielectric section having a diameter of 103 Ω·cm to 1.
08 Ω·cm of resistance, and the dielectric portion is formed in a foam cell near the surface of the conductive foam layer, and at least the dielectric portion is formed in a foam cell near the surface of the conductive foam layer. is charged to the opposite polarity or the same polarity as the polarity of the developer, thereby forming a large number of minute electric fields on the surface, and the bias applying means applies a peak to the developing area.
topeak is 500≦Vp-p≦1500 (v)
applying a bias that forms an alternating electric field, and controlling the movement of the developer by an electric field determined by the mutual relationship between the potential on the image carrier, the electric field due to the bias, and the electric field on the developer carrier. The invention according to claim 2 is characterized in that, instead of the dielectric part being formed in a foam cell near the surface of the conductive foam layer, the conductor part and the dielectric part are formed in the foam cell. The invention of claim 3 is characterized in that it is made of an elastic conductive material containing insulating particles, and the invention of claim 3 is characterized in that
In addition to the feature of the invention of claim 4, the insulating particles are elastic insulating particles.
In addition to the features of the invention described in Items 3 to 3, the frequency of the alternating electric field is 250 to 2000 Hz.

[0024]

[Operation] According to the present invention, in the invention of claim 1,
Since the developer carrier is formed by mixing a conductor part having a resistance within a predetermined range and a dielectric part in a small area, a minute closed electric field is formed between the conductor part and the dielectric part, A strong developer adsorption force is generated, and a large amount of developer is attached to the surface. In this case, the developer is rubbed between the developer carrier and the member that supplies the developer, becomes strongly charged, adheres to the conductor part, and is strongly attracted to the dielectric part, forming a multilayer. The developer adheres to the developer and is transported to the developing section with its layer thickness regulated by a developer layer thickness regulating member, etc., and as a result, sufficient developer can be transferred to the image carrier. Further, the adhesion and charging of the developer are stable over time. Furthermore, the image forming cost becomes low.

Furthermore, since the conductor part and the dielectric part are formed by forming the dielectric part in the foamed cells near the surface of the conductive foam layer, the developer carrier can be easily formed by using the foaming process. By changing the degree of foaming, the area and depth of the dielectric part can be changed to freely adjust the adhesion of the developer. Furthermore, since the foaming is random, the charging and adhesion of the developer can be easily adjusted. No regular irregularities occur.

Furthermore, since a bias is applied to the developing section to form an alternating electric field, when an electric field is generated on one side, the holding force due to the minute closed electric field is resisted in response to the potential of the electrostatic latent image on the image carrier. At the same time, when an electric field is generated on the other side, the developer flies from the image carrier to the developer carrier due to the opposite development. Fly backwards. And this bias voltage pea
The difference between k to peak is 500≦Vp-p≦15
By setting the value within the range of 00(v), the developer can be reliably flown without causing background fog, and the phenomenon of the developer flying in both directions is ensured. The developer is transferred to the body in accordance with the potential, and the gradation of the image is realized.

In this case, since the dielectric portion is charged, the electric potential is different between the conductive portion and the dielectric portion, and the developer is held in multiple layers in the dielectric portion. By setting the potentials of the image carrier and developer carrier and the values of the alternating electric field due to the bias to good conditions in relation to each other, the final transferability of the developer from the developer carrier to the image carrier can be improved. image density is improved and sufficient image density is ensured. Moreover, the clarity of the image can also be obtained.

In the invention according to claim 2 or 3, the conductor part and the dielectric part are made of an elastic conductive material containing insulating particles, or the insulating particles are made into elastic insulating particles. The image carrier is not damaged even when contact development is performed.

In the invention of claim 4, since the frequency of the alternating electric field is set to 250 to 2000 Hz, the bias drop and the relationship between the contact length between the developer carrier and the image carrier and the rotational speed of the image carrier are reduced. The occurrence of image density unevenness due to the bias cycle is prevented, and the development between the developer carrier and the image carrier is prevented in relation to the flight time of the developer between the developer carrier and the image carrier. The time for the reciprocating movement of the agent is ensured, and the effect of flying development is ensured.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of a developing device to which the present invention can be applied. The developing device is disposed facing the photoreceptor 10, which is an example of an image carrier. toner tank 70
The toner 60 as a developer contained in the toner is forcibly moved toward the toner supply member (such as a sponge roller or a fur brush) 40 by the stirring blade 50 and is supplied thereto. On the other hand, the developing roller 20 as a developer carrier that has completed development rotates in the direction of the arrow (for example, 400
rpm) and reaches the contact portion with the toner supply member 40. The toner supply member 40 rotates in the opposite direction to the developing roller 20 (for example, at 300 rpm), and the toner supplying member 40 rotates in the opposite direction to the developing roller 20 (for example, at 300 rpm).
Toner 60 is applied onto the developing roller 20 by applying a charge to the developing roller 20. Further, the developing roller 20 rotates, and the toner adhering thereto is removed by the elastic blade 3, which is a developer layer thickness regulating member.
0, the thickness is controlled and the charging is stabilized,
The development area 80 is reached. In the development area 80, the latent image is developed by contact or non-contact development. Here, if necessary, direct current may be applied to the developing roller 20 and the toner supply member 40.
By applying bias such as alternating current, direct current superimposed alternating current, pulse, etc., it is possible to control the optimum image.

Next, the mechanism of toner adhesion to this type (electrode type) developing roller 20 will be explained. As the developing roller 20, for example, as shown in FIG.
A dielectric region (dielectric part 22) and a conductive region (
The conductor portions 21) are configured to coexist in a small area. When the shape of the dielectric portion is circular, minute areas with a diameter of 10 to 500 μm are dispersed randomly or according to a certain regulation. in this case,
As for the area ratio, the area of the conductor portion 21 is 20 to 6 of the total area.
The range is preferably 0%.

Toner adhesion is as follows. First, the developing roller 20 that has completed development rotates in the direction of the arrow and comes into contact with the toner supply member 40 . The remaining toner in the non-image area that has not been developed is mechanically and electrically scraped off by the toner supply member 40, and the dielectric portion 22 is charged by friction. At this time, the charges on the developing roller 20 and the toner due to the previous development are made constant and initialized by friction. Next, the toner transported by the toner supply member 40 is
It is strongly charged due to friction with the developing roller 20, and electrostatically adheres strongly in large quantities to the dielectric portion 22 together with the conductive portion 21 of the developing roller 20. At this time, the polarity of the toner is opposite to the charge on the photoreceptor, and the dielectric portion 2 of the developing roller 20
2 has the same polarity.

FIG. 2 shows the formation of an electric field on the developing roller 20 and the state of toner adhesion. The electric field on the developing roller 20 is
It becomes a micro field (closed electric field) and an electric field with a large electric field gradient, making it possible to deposit a large amount of toner. This adhered toner is strongly attracted to the developing roller 20 by the closed electric field and is difficult to separate. The thickness of this toner layer is further regulated by the elastic blade 30 and reaches the developing section 80 .

In FIG. 1, a photoreceptor 10 and a developing roller 2
0, a developing bias is applied to the developing section 80 by a bias applying means 90 that forms an alternating electric field. As for the developing bias, peak to peak is 5.
00≦Vp-p≦1500 (v) and a direct current can be superimposed on an alternating current electric field. The reason why Vp-p is set to 500V or more is because a voltage difference of this level or more is required to make the toner fly to the photoreceptor 10 against the toner retention force of the developing roller 20. 150
The purpose of setting the voltage below 0 V is to prevent bias leakage and background fog, and it has been experimentally confirmed that this range is appropriate.

[0035] Also, the frequency of the developing bias is 250 to 20
00Hz range. This is because when the frequency is below 250 Hz, image unevenness due to bias occurs and the image quality is degraded, while when the frequency is above 2000 Hz, the flight time of the toner between the developing roller 20 and the photoreceptor 10 cannot be obtained. This is because the effect of forming an alternating electric field is substantially lost.

[0036] Figures 3 to 5 show that within the range of the above conditions,
FIG. 3 is a diagram specifically defining the potential of the photoconductor 10, the bias electric field, and the electric field of the developing roller 20 as an example, and explaining the movement of toner due to the electric field determined by the mutual relationship between these. In this specific example, the surface potential of the background of the photoreceptor is -9
The developing roller 20 shown in FIG. 2 was brought into contact with the surface of the photoreceptor 10 (10
(may be spaced apart by about 0 μm), and reversal development is performed by disposing them facing each other.

The dielectric portion 22 of the developing roller 20 is rubbed by the toner supply member 40, and its potential with respect to the ground increases by +200.
It held an amount of charge equal to V, thereby supporting approximately 1.0 to 1.2 mg/cm 2 of negatively charged toner. Then, by applying a bias to the developing roller 20,
Vp-p=1000V, highest potential 0V, frequency 500H
z, duty ratio (ratio of time for applying voltage so that toner is transferred to the developing side with respect to one cycle of alternating bias; expressed as T1 and T2 shown in FIG. 3, T2
A rectangular pulse voltage of /T1 )=0.5 was applied.

FIG. 3 shows the developing roller 20 with reference to grounding.
2 is a diagram showing temporal changes in surface potential of the dielectric portion 22, (a) shows the surface potential of the dielectric portion 22, and (b) shows the surface potential of the conductor portion 21. FIG. In these figures, the photoreceptor 10
The surface potential level of −900 V at the background portion of the surface and the surface potential level of −100 V at the exposed portion are shown as horizontal lines, respectively. As can be seen from the continuous rectangular line showing the temporal change in the surface potential of the dielectric portion 22 in FIG. becomes a potential biased by +200V. On the other hand, as can be seen from FIG. 3B, the surface potential of the conductor portion 21 is the same as the voltage applied by the bias applying means 90 since there is no retained charge.

Next, the relationship between the developing roller 20 and the photoreceptor 1 when the surface potential of the developing roller 20 changes as described above.
The electric field between 0 and 0 will be explained. This electric field is generated depending on which part of the developing roller 20 is on the dielectric part 22 or the conductive part 21, and whether the part of the photoreceptor 10 facing each part 22, 21 is the image part or the background part. It depends on whether

FIG. 4 is a diagram for explaining the electric field on the conductor portion 21 that causes a temporal change in the surface potential as shown in FIG. 3(b). It shows the temporal change in the potential difference between the portion 21 and the image portion (exposed portion) of the photoreceptor 10, and (
b) shows a temporal change in the potential difference between the conductor portion 21 and the non-image portion (unexposed portion) of the photoreceptor 10 when the conductor portion 21 faces the non-image portion (unexposed portion).

On the other hand, FIG. 5 is for explaining the electric field on the dielectric portion 22 that causes the temporal change in surface potential as shown in FIG. 3(a). FIG. 12(b) shows a temporal change in the potential difference between the portion 22 and the image portion (exposed portion) of the photoreceptor 10 when the dielectric portion 22 faces the non-image portion (unexposed portion) of the photoreceptor 10. Fig. 3 shows the temporal change in the potential difference between the two when they are facing each other.

In these figures, since the electric field exerts an electrostatic force on the toner carried on the surface of the developing roller 20 or the photoreceptor 10, in order to distinguish the direction of this electrostatic force, it is shown that the toner moves toward the photoreceptor 10. The potential difference corresponding to the electric field in the direction is expressed as positive, and the potential difference corresponding to the electric field in the direction toward the developing roller 20 is expressed as negative. Also, the developing roller 2
The threshold value +100V is the limit value of the potential difference at which the toner on the photoreceptor 10 transfers to the photoreceptor 10, and the electric field threshold −100V level at which the toner on the photoreceptor 10 transfers to the developing roller 20. are each indicated by a horizontal line, and
The part of the potential difference corresponding to the electric field that contributes to toner transfer exceeding this threshold is indicated by diagonal lines.

[0043] Note that the above threshold values are +100V and -10V.
0V is a value determined by experiment. In this experiment, a DC voltage was applied to the developing roller 20, and the transfer of toner was observed while changing the value of this DC voltage. In this example, the threshold value of the developing electric field is 1V/μm.
It turned out to be. Further, the amount of charge of the toner used at this time was about 10 μC/g.

When the toner existing on the conductive portion 21 of the developing roller 20 faces the image portion of the photoreceptor 10,
As shown by the hatched area in FIG. 4(a), when a developing electric field corresponding to a potential difference of +900V (hereinafter referred to as "developing electric field") is generated, it is transferred in the direction of the photoreceptor 10 and is opposed to the background part of the photoreceptor 10. In this case, as shown by the hatched area in FIG. 2B, when a developing electric field of -900 V is generated, the toner is transferred in the direction of the developing roller 20. In these cases, the toner in the image area will not be reversely transferred to the developing roller 20 side, and the toner in the non-image area will not be transferred to the photoreceptor 10 side.

On the other hand, the toner existing on the dielectric portion 22 of the developing roller 20 is exposed to an applied voltage of +200V in this portion.
Therefore, when facing the image area of the photoreceptor 10, a negative electric field of -300V and a positive electric field of +700V alternate as shown by the shaded area in FIG. 5(a). Therefore, it is transferred from the developing roller 20 to the photoreceptor 10 when the electric field is positive, and from the photoreceptor 10 to the developing roller 20 when the electric field is negative. In addition, when facing the background part of the photoreceptor 10, as shown by the hatched part in FIG.
Toner is only transferred from the photoreceptor 10 to the developing roller 20 by a negative electric field of 100V, and the toner in the non-image area is not transferred to the photoreceptor 10 side.

As described above, according to the present invention, the electric field determined by the interrelationship between the electric field due to the bias, the potential of the photoreceptor 10, and the potentials of the conductive portion 21 and the dielectric portion 22 of the developing roller 20 is used. , can selectively transfer toner.

That is, by setting these mutual relationships under good conditions as in the concrete example, for example, in the conductor portion 21,
For the image area, toner is transferred from the developing roller 20 only to the photoreceptor 10, increasing the amount of toner development without reverse transfer, and in the dielectric area 22 where toner is attached in multiple layers, the toner is transferred only to the photoreceptor 10. By alternately transferring the toner and making the amount of toner transferred corresponding to the potential difference, it is possible to obtain gradation of an image. When the conductor part 21 and the dielectric part 22 face the non-image part, the photoreceptor 1
By reversely transferring the toner adhering to the non-image area of 0, there is no background smudge and the sharpness of the image is improved. As a result, the toner development transfer rate was 90% or more, and an image with sufficient image density and good sharpness and gradation was obtained.

In the above specific example, the alternating bias is a rectangular bias voltage with a duty ratio of 0.5, but the duty ratio is not limited to 0.5, and the waveform may be a sine wave or other waveform. It may be a waveform.

Next, the developing roller 20 will be explained in detail. First, a case will be described in which a developing roller has a dielectric portion and a conductive portion coexisting in a small area on its surface, and the dielectric portion is formed in foam cells near the surface of a conductive foam layer.

The material used for the dielectric portion formed in the foam cell may be any insulating material, but the material has a volume resistivity of 1012 Ω·cm or more, particularly 1014 Ω·cm.
The above are preferred.

Examples of such insulating materials include the following organic polymers: vinyl resins such as polyvinyl chloride, polyvinyl butyral, polyvinyl alcohol, polyvinylidene chloride, polyvinyl acetate, and polyvinyl formal; Polystyrene resins such as polystyrene, styrene/acrylonitrile copolymer, acrylonitrile/butadiene/styrene copolymer; polyethylene resins such as polyethylene, ethylene/vinyl acetate copolymer; polymethyl methacrylate, polymethyl methacrylate/styrene copolymer Acrylic resins such as polyacetal, polyamide, cellulose, polycarbonate, phenoxy resin, polyester, fluororesin, polyurethane, phenol resin, urea resin, melamine resin, epoxy resin, unsaturated polyester resin, silicone resin and other resin materials; natural rubber , isoprene rubber, butadiene rubber, styrene/butadiene rubber, butyl rubber, ethylene/propylene rubber, chloroprene rubber, chlorinated polyethylene rubber, epichlorohydrin rubber, nitrile rubber, acrylic rubber, urethane rubber, polysulfide rubber, silicone rubber, fluororubber, etc. rubber materials etc.

In the present invention, it is preferable to use a material mainly composed of an aliphatic fluorine-containing compound or a silicone resin.

Examples of aliphatic fluorine-containing compounds include polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene/hexafluoropropylene copolymer, tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer, and tetrafluoroethylene/ethylene copolymer. Polymers, fluorine-containing polymers such as polychlorotrifluoroethylene, and aliphatic fluorocarbons and aliphatic fluorochlorocarbon compounds having polar groups such as ether groups, carboxyl groups, and hydroxyl groups at the end of the molecular chain or in the molecular chain. It will be done. Examples of the silicone resin include condensation reaction type, addition reaction type, and peroxide curing reaction type silicone resins, as well as modified resins obtained by copolymerizing organic resins.

The conductive portion in the present invention is composed of a conductive foam layer, but various organic polymers can be used as the resin material forming the foam, such as the following organic polymers: Examples include: natural rubber, isoprene rubber, putadiene rubber, styrene-putadiene rubber,
Rubber materials such as butyl rubber, ethylene/propylene rubber, chloroprene rubber, chlorinated polyethylene rubber, epichlorohydrin rubber, nitrile rubber, acrylic rubber, urethane rubber, polysulfide rubber, silicone rubber, fluororubber, silicone-modified ethylene/propylene rubber, etc.

[0055] Examples of conductivity imparting agents include metal powders such as Ni and Cu; carbon blacks such as furnace black, lamp black, thermal black, acetylene black, and channel black; tin oxide, zinc oxide, molybdenum oxide, and antimony oxide. , conductive oxides such as potassium titanate; electroless plated materials plated on titanium oxide, mica, etc.; graphite, metal fibers, carbon fibers, etc.

Further, as the blowing agent, any conventionally known organic blowing agent or inorganic blowing agent can be used. Specific examples of such blowing agents include azobisisobutyronitrile, azodicarbonamide, benzenesulfonylhydrazide, p,p'-oxybisbenzenesulfonylhydrazide, and the like.

To produce the developing roller of the present invention, for example, (i) extrusion molding a conductive foam composition comprising rubber, a conductive agent, a foaming agent, and other additives on the outer periphery of a core metal; Then, the surface of the elastic foam layer is ground to expose the foam cells, a recess for embedding the dielectric part is formed, and then the dielectric material is embedded in the recess by a method such as spraying or dipping. , given conditions (temperature, time)
(the thickness of the coating film should be such that it completely fills the recesses) [see Figure 6(a)], and (ii) the surface is then cut or polished to form a conductive surface and a dielectric surface. The area of the conductive part is 20 to 60.
% [see FIG. 6(b)].

[Example of developer carrier] The above-mentioned developer carrier will be explained in more detail below using an example. Note that parts are based on weight. [Example-1] The following conductive foam composition [I] was extruded around the core metal which had been previously treated with a primer, and heated at 170°C.
After temporarily curing in the mold for 20 minutes at 200°C,
After time secondary vulcanization, volume resistivity 1011Ω・cm,
A developing roller having a conductive foam layer having a specific gravity of 0.57 and a foam cell size of 30 to 50 μm was prepared.

Conductive foam composition [I] Diorganopolysiloxane (average degree of polymerization 2000 or more) 100 parts [Product name: KF90
1F-U (manufactured by Shin-Etsu Chemical) Furnace black

10 copies [Product name: Ketjen Black EC (manufactured by Lion Akzo)]
dicumyl peroxide

Part 2 Azobisisobutyronitrile

2 parts Then, the surface of the obtained developing roller was ground to expose the foamed cells, and a recessed part for embedding the dielectric material was formed.

Next, 150 parts of a dielectric fluororesin composition [product name: Lumiflon LF601-C (manufactured by Asahi Glass Co., Ltd.] as the main ingredient) was coated on the recessed portions until the foamed cell recessed portions were completely filled. After that, it was crosslinked and cured.

[0061] Subsequently, by cutting or polishing the surface, the conductor part and the dielectric part are mixed, and the conductor part area is 50 mm.
% of the developing roller of the present invention.

[Example-2] In Example 1, the conductive foam composition [I] was replaced with the conductive foam composition [II], and the volume resistivity was 106 Ω·cm, the specific gravity was 0.31, and the size of the foam cells was A developing roller of the present invention was produced in the same manner as in Example 1, except that a developing roller having a conductive foam layer of 90 to 120 μm was used.

Conductive foam composition [II] Diorganopolysiloxane (average degree of polymerization 2000 or more) 100 parts [Product name: KF90
1F-U (manufactured by Shin-Etsu Chemical) Furnace black

30 copies [Product name: Ketjen Black EC (manufactured by Lion Akzo)]
dicumyl peroxide

5 parts Azobisisobutyronitrile

10 parts [Example-3] In Example 1, the conductive foam composition [I] was replaced with the conductive foam composition [III], and the volume resistivity was 102 Ω・cm, the specific gravity was 0.23, and the size of the foam cell was 200. A developing roller of the present invention was produced in the same manner as in Example 1, except that a developing roller having a conductive foam layer of ~460 μm was used.

Conductive foam composition [III] Diorganopolysiloxane (average degree of polymerization 2000 or more) 100 parts [Product name: KF90
1F-U (manufactured by Shin-Etsu Chemical) Furnace black

50 copies [Product name: Ketjen Black EC (manufactured by Lion Akzo)]
dicumyl peroxide

10 parts azobisisobutyronitrile

14 parts [Example 4] In Example 1, the fluororesin as a dielectric was added to the addition type silicone resin composition [Product name: S
R2407 (manufactured by Toray Silicone)], Example 1
A developing roller of the present invention was produced in the same manner as described above.

[Example 5] In Example 2, a fluororesin as a dielectric was added to an addition type silicone resin composition [trade name:
A developing roller of the present invention was produced in the same manner as in Example 1, except that SR2407 (manufactured by Toray Silicone Co., Ltd.) was used.

[Example 6] In Example 3, a fluororesin as a dielectric was added to an addition type silicone resin composition [trade name:
A developing roller of the present invention was produced in the same manner as in Example 1, except that SR2407 (manufactured by Toray Silicone Co., Ltd.) was used.

[Evaluation of Examples 1 to 6] Each developing roller was attached to the developing device shown in FIG. 1, and the toner charge amount and toner adhesion amount were measured. The results are shown in Table 1.

In the above-mentioned developing device, the elastic blade was made of urethane rubber, the toner supply member was made of conductive urethane sponge, and positively charged toner was loaded.

[0069]

[Table 1]

From the results in Table 1, it can be seen that the developing roller of the present invention provides sufficient toner charge and adhesion.

[0071] Next, in the case where the developing roller has at least the conductor part 21 and the dielectric part 22 mixed on its surface, and the material forming these parts is an elastic conductive material containing elastic insulating particles. I will explain about it.

The elastic insulating particles constituting the dielectric part have a volume resistivity of 1013 Ω·cm or more, preferably 10
14 Ω・cm or more, and the effective rubber hardness (the value when the shape of the developer carrier is measured using a spring-type hardness tester type A specified in JIS-K6301) is 50 degrees or less, preferably 40 degrees. The following are used:

Examples of such materials include silicone-modified ethylene propylene rubber, epichlorohydrin rubber, butyry rubber, silicone rubber, and ethylene propylene rubber. The average particle size is 5 μm or more, preferably 10 μm or more. If it is less than 5 μm, it is difficult to form a microfield, and stable toner adhesion and charging cannot be obtained. Further, the particle shape may be either regular or amorphous.

[0074] The elastic conductive material preferably has a volume resistivity of 1012 Ω·cm or less, preferably 108 Ω·cm or less, and has an effective rubber hardness (as described above) of 50 degrees or more, preferably 40 degrees or less. Rubbers with conductive fillers added are used.

Examples of rubbers include silicone-modified ethylene propylene rubber, styrene-putadiene rubber, epichlorohydrin rubber, ethylene-propylene rubber, urethane rubber, fluororubber, silicone rubber, nitrile rubber, acrylic rubber, butyl rubber, and isoprene rubber.

[0076] Also, as the conductive filler, Ni, Cu
Metal powder such as furnace black, lamp black,
Carbon black such as thermal black, acetylene black, and channel black; Conductive oxides such as tin oxide, zinc oxide, molybdenum oxide, antimony oxide, and potassium titanate; Electroless plated materials such as titanium oxide and mica. ; Examples include graphite, metal fiber, carbon fiber, etc.

Further, inorganic fillers, crosslinking agents, heat stabilizers, processing aids, etc. can be added to the developing roller used in the present invention for various purposes. Inorganic fillers include diatomaceous earth, quartz powder, iron oxide, zinc oxide, titanium oxide, calcium oxide, magnesium oxide, talc, aluminum silicate, aluminum oxide powder, potassium titanate, asbestos, glass, carbon fibers, etc. ,Teflon,
Powder such as boron nitride is used.

In order to manufacture the developing roller of the present invention, for example, (i) a conductive primer is applied onto a metal core, and then a compound in which an appropriate amount of insulating particles are mixed into a conductive material is extruded. Formed on the core metal using a molding method etc., (ii
) An elastic roller is formed on the core metal by applying temperature and pressure using mold molding vulcanization, steam vulcanization, etc., and (ii
i) Next, a method may be adopted in which the surface of the elastic roller is smoothed by a method such as polishing or cutting so that the conductive portion and the dielectric portion are mixed on the surface.

[Example] Next, the developing roller will be explained in more detail using an example. [Manufacture of elastic insulating particles] Silicone-modified ethylene/propylene rubber: Product name: SEP1421-U (Shin-Etsu Chemical Co., Ltd.)
Co., Ltd.) 100.0 parts by weight Vulcanizing agent: Product name; C
-12 (manufactured by Shin-Etsu Chemical Co., Ltd.)
2.0 Use two rollers to knead the mixture until it is sufficiently uniform, then press cure at 170°C for 10 minutes for 50 minutes.
It was vulcanized under vulcanization conditions of kg/cm2 and formed into a sheet with a thickness of 2 mm. Thereafter, curing was performed at 150°C for 2 hours.

The formed rubber sheet was passed through two rollers (the gap between the rollers was narrowed) several times to be crushed. Thereafter, it was passed through a sieve to obtain elastic insulating particles of 100 to 200 μm.

[Production of elastic conductive compound containing elastic insulating particles] Silicone-modified ethylene/propylene rubber:
Product name; SEP1421-U (manufactured by Shin-Etsu Chemical Co., Ltd.) 100.0 parts by weight Carbon black: Product name; Black Pearls L (manufactured by Cabot Corporation) 8.0 Vulcanizing agent: Product name; C-12 (manufactured by Shin-Etsu Chemical Co., Ltd.) (manufactured by Kagaku Kogyo Co., Ltd.)
4.0 〃 Hydrocarbon-based synthetic oil: Product name: Lucant (manufactured by Mitsui Petrochemical Co., Ltd.)
10.0 was kneaded using two rollers until it was sufficiently uniform. To this kneaded compound, 30.0 parts by weight of the elastic insulating particles produced previously were added. Then, the mixture was kneaded again using two rollers until it was sufficiently uniform, to obtain an elastic conductive compound.

[0082] Next, a conductive compound containing the elastic insulating particles was applied by extrusion molding onto a core metal coated with a conductive primer in advance, and then press cured at 170°C for 10 minutes by a mold molding vulcanization method. ,50kg/cm
After vulcanization under the conditions of 2, the elastic layer was formed to have a thickness of 7 mm and a roller outer diameter of 20 mm (core: stainless steel, 6 mm), and then cured at 150°C for 2 hours.

The surface of the obtained elastic roller is polished or cut to form a developing roller (effectively A rubber hardness of 38 degrees) was obtained.

Next, the obtained developing roller was installed in the developing device shown in FIG. 1, and the toner charge amount, toner adhesion amount, and contact width with the photoreceptor [mm/pressure (kg)] were measured. .

As a result, the toner charge amount was 12.3 μC/
g, the toner adhesion amount is 1.06 mg/cm2, and the contact width with the photoreceptor is 0.8 mm/500 g, 1.1 mm/cm2.
It was 800g, 1.6mm/1.1kg.

In the above-mentioned developing device, the elastic blade was made of urethane rubber, the toner supply member was made of conductive urethane sponge, and the toner was charged with positively charged toner.

[0087]

As described above, according to the present invention, in the invention of claim 1, the conductor part and the dielectric part are mixed in a small area to form the developer carrier, so that a small closed area is formed between the conductive part and the dielectric part. An electric field is created and a large amount of developer can be deposited on the surface.

[0088] Since the conductor part and the dielectric part are formed by forming the dielectric part in the foam cells near the surface of the conductive foam layer, the developer carrier can be manufactured easily. By randomly changing the area and depth of the dielectric portion, it is possible to uniformly and freely adjust the charging and adhesion of the developer.

Furthermore, a bias that forms an alternating electric field is applied to the developing section, and the peak to
Since the difference in peak is set in the range of 500≦Vp-p≦1500 (v), it is possible to ensure the flying phenomenon of the developer in both directions between the developer carrier and the image carrier without causing background fog. As a result, the developer can be transferred from the developer carrier to the image carrier in accordance with the potential thereof, and the gradation of the image can be obtained.

In this case, since the dielectric portion is charged, the potential is different between the conductive portion and the dielectric portion, and the dielectric portion holds developer in multiple layers. The final transferability of the developer from the developer carrier to the image carrier can be improved, sufficient image density can be ensured, and the image can be made clearer.

In the invention of claim 2 or 3, in addition to the above effects, the conductor portion and the dielectric portion are made of an elastic conductive material containing insulating particles, or the insulating particles are made of an elastic insulating material. By forming the particles into particles, damage to the image carrier can be prevented even when contact development is performed.

In the invention of claim 4, since the frequency of the alternating electric field is set to 250 to 2000 Hz, it is possible to prevent the occurrence of density unevenness in the image due to the bias cycle, and also to prevent the occurrence of uneven density between the developer carrier and the image carrier. The effect of flying development can be ensured.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of a developing device according to an embodiment.

FIG. 2 is an explanatory diagram showing a phenomenon in which toner adheres to a developing roller.

FIGS. 3(a) and 3(b) are curve diagrams showing changes in surface potential of a dielectric portion and a conductive portion, respectively.

FIGS. 4(a) and 4(b) are curve diagrams showing electric fields in an image area and a non-image area, respectively, in a conductor part.

FIGS. 5(a) and 5(b) are curve diagrams showing electric fields in an image area and a non-image area, respectively, in a dielectric part.

FIGS. 6(a) and 6(b) are explanatory views showing the manufacturing process of the developing roller.

[Explanation of symbols]

10 Photoreceptor (image carrier) 20 Developing roller (developer carrier) 80 Developing section 90 Bias application means

Claims (4)

[Claims] 1. Development in which an image carrier carrying an electrostatic latent image and a developer carrier carrying a developer are opposed to each other in a developing section, and a bias is applied to the developing section by a bias applying means to perform development. In the device, the developer carrier includes:
Dielectric part on the surface and 103 Ω・cm to 108 Ω・cm
, and the dielectric portion is formed in the foam cells near the surface of the conductive foam layer, and at least the dielectric portion has a resistance of A large number of minute electric fields are formed on the surface by being charged to the opposite polarity or the same polarity, and the bias applying means applies a peak topea to the developing section.
Applying a bias that forms an alternating electric field where k is 500≦Vp-p≦1500 (v), and determining the interaction between the potential on the image carrier, the electric field due to the bias, and the electric field on the developer carrier. A developing device characterized in that movement of the developer is controlled by a determined electric field. 2. Development in which an image carrier carrying an electrostatic latent image and a developer carrier carrying a developer are opposed to each other in a developing section, and a bias is applied to the developing section by a bias applying means to perform development. In the device, the developer carrier includes:
Dielectric part on the surface and 103 Ω・cm to 108 Ω・cm
and a conductor part having a resistance of A large number of minute electric fields are formed on the surface by charging, and the bias applying means is
Peak to peak in the developing section is 500≦
Applying a bias that satisfies Vp-p≦1500 (v) and forming an alternating electric field, and an electric field determined by the mutual relationship between the potential on the image carrier, the electric field due to the bias, and the electric field on the developer carrier. A developing device characterized in that the movement of the developer is controlled by. 3. The developing device according to claim 2, wherein the insulating particles are elastic insulating particles. 4. The frequency of the alternating electric field is 250 to 20
Claims 1 to 3 characterized in that the frequency is 00Hz.
The developing device described in .